1. Field of the Invention
The present invention relates to a channel estimator and related method, and more particularly, to a channel estimator and related method for smoothing a channel response of a multi-carrier communication system.
2. Description of the Prior Art
The communication channel between a receiver and a transmitter delays and attenuates the transmitted signal. As a result, the amplitude of a received signal is smaller than the amplitude of the corresponding transmitted signal, and the phase of the transmitted signal is different from the phase of the received signal. To alleviate the phenomenon mentioned above, an equalizer and a channel estimator are implemented in the receiver to restore the attenuated and delayed signal received from the communication channel. Firstly, the channel estimator evaluates the attenuation and the delay of the received signal according to a preamble of the received packet, where the preamble is a series of known symbols. That is, the channel estimator generates a channel estimating value by comparing the received signal with the known symbols. The operation of the channel estimator is shown in the following equation:
                              H          ′                =                  R          X                                    Equation        ⁢                                  ⁢                  (          1          )                    
In the equation (1), R denotes the received signal, X denotes the known preamble, and H′ denotes the channel estimating value.
After a plurality of channel estimating values H′, H″, . . . ,H′(n) corresponding to the same sub-channel are generated then a channel response Ĥ of the communication channel is produced by computing a mean value of the plurality of channel estimating values H′, H″, . . . H′(n). Please note that, H′ denotes a channel estimating value produced by utilizing a first symbol of the preamble, and the channel estimating value H″ denotes a channel estimating value produced by utilizing a second symbol of the preamble. The first symbol and the second symbols correspond to a first time interval and a second time interval, respectively. In the same manner, H′(n) denotes a channel estimating value produced by utilizing an n-th symbol of the preamble corresponding to an n-th time interval. Because of noise, the channel estimating values generated in different time intervals correspond to different values. Finally, the equalizer utilizes an inverse function of the channel response Ĥ to restore the received signal R thereby generating an equalized signal. The equalized signal is no longer distorted by the communication channel and is considerably equal to the original transmitted signal.
In the multi-carrier communication system, such as an ultra-wideband (UWB) communication system, the channel responses of two adjacent sub-carriers are correlated such that the channel responses of different sub-carriers will form a smoothed curve in a spectrum. Unfortunately, the wireless communication system suffers from noise. The noise reduces the signal to noise ratio (SNR) of the wireless communication system. Owing to the noise of the communication channel, the estimated channel responses are incorrect. The resulting curve containing the incorrect channel responses displays jitters. Furthermore, it is not possible to utilize these incorrect channel responses in an effort to restore the received signal in hopes of generating the equalized signal.